This slides describe biochemical properties, function of potassium and utilization, metabolism of Potassium

1. BIOCHEMICAL FUNCTION AND
METABOLISM OF POTASSIUM
Md. Redoan Akond Sumon
Scientific Officer (Feed Quality Control)
Bangladesh Livestock research Institute (BLRI),
Savar, Dhaka-1341
Cell: +8801747481116
Email: redoanakond@gmail.com

2. POTASSIUM
 Potassium is an essential plant nutrient and is
required in large amounts for proper growth and
reproduction of plants
 It affects the plant shape, size, color, taste and other
measurements attributed to healthy produce
 Plants absorb K in its ionic form, K+
 K+ is an univalent cation with a hydrated ionic
radius of 0.331 nm and Hydration energy of 314 J/mol
 High mobility in plants
 Have utstanding role in plant–water relations

3. Compartmentation and Cellular
Concentrations
 Concentrations generally 100– 200 mM, but Vary between 10
and 200 mM or up to 500 mM
 membrane proteins required to facilitate movement of K+
through membranes
 K+ and Ca2+ channels are similar in principle but different in
function.
 K+ ions act directly as solutes, changing the osmotic potential
in the compartments and thereby turgor, and, as carrier of
charges, also the membrane potential.

4. Enzyme Activation
 The enzyme catalyses the transfer of glucose to starch molecules
ADP-Glucose +starch ↔ADP + glucosyl - starch
Figure 1: Activity of ADP-glucose starch synthase from maize with supply of different univalent
cations

5. Figure 2: Concentrations of selected metabolite in roots of Arabidopsis induced
by low K supply for 14 days and resupply of K for 24 h. From Armengaud et al.
(2009) with permission from the American Society of Plant Biologists.

6. Figure 3: (A)Carbon exchange rate (CER), (B) transpiration, (C) stomatal
resistance, and (D) internal CO2 in soybean plants under K deficiency. Adapted
from Huber (1984)

7. Protein Synthesis
 K+ involves in translation process
 Required in higher concentrations for protein synthesis than for enzyme activation
 Activates and helps to synthesis nitrate reductase enzyme
 Synthesis of enzyme is impaired under K+ deficiency and responds rapidly to resupply of K
Table 1: Incorporation of 14C-leucine into RuBP carboxylase in the
leaves of K-deficient alfalfa plants pre-incubated at different K
concentrations in the light for 20 hours

8. Photosynthesis
 Affects photosynthesis via stomatal regulation
 Leaf mesophyll resistance is more important than stomatal resistance
 Role of K+ in CO2 fixation has been most clearly demonstrated with
isolated chloroplasts
Table 2: Relationship between K concentration in
leaves, carbon dioxide exchange, RuBP carboxylase
activity, photo and dark respiration in lucerne
With decreasing leaf K concentration,
not only the rate of photosynthesis
and RuBP carboxylase activity, but
also photorespiration is decreased

9. Osmoregulation
Cell Extension
•Enarge central vacuole at 80–90% of the cell volume.
Figure 4: Model of the role of K and other solutes in cell
extension and osmoregulation.
K+; □: reducing sugars, sucrose
Na+; ●:organic acid anions

10. Stimulation of stem elongation by gibberellic acid (GA) is
dependent on K supply
Table 3: Plant height and concentrations of sugars and K in the shoots
of sunflower plants at different K and gibberellic acid (GA) supply

11. Stomata Movement
Increasing K+ concentration in the guard cells increases osmotic pressure
 results in the uptake of water from the adjacent cells
results in an increase in turgor in the guard cells and thus stomata opening
Table 4: Relationship between stomatal aperture and characteristics of
guard cells of faba bean

12. Opening stomata can be shown by X-ray microprobe analysis
FIGURE 5: Electron-probe analyser image (top) and corresponding X-ray microprobe
images of K distribution (bottom) in open and closed stomata of faba bean. Courtesy
of B. Wurster.

13. Metabolic and transport systems involved in stomata opening
Figure 6: Schematic diagram of possible osmoregulatory pathways in guard cells for stomata
opening. The diagram is not to scale. For explanations see text. Inspired by and redrawn from
Roelfsema and Hedrich (2005) and Lawson (2009).
DHAP= dihydroxyacetonphosphat; PEP= phosphoenolpyruvate; OAA = oxalacetate.

14. Photonastic and Seismonastic Movements
 Leguminosae and other plants response to light signals
 Responses either increase light interception or allow avoidance of
damage by excess light
 principles of the mechanisms responsible for stomata movement
 Seismonastic signals
 In Mimosa pudica, the leaflets fold within a few seconds and reopen
after about 30 min

15. Phloem Transport
 K plays a critical role in phloem transport
Figure 7: Phloem Transport system in plant

16. Energy Transfer
Figure 8: Photosynthesis of leaves at declining leaf water potentials in
wheat at different K supply (mM). Based on Sen Gupta et al. (1989).

17. K Supply, Plant Growth and Plant
Composition
 K requirement for optimal plant growth is 20–50 g/kg in
vegetative parts, fleshy fruits and tubers.
 When K is deficient, growth is retarded
 Under severe deficiency plant organs become chlorotic and
necrotic in condition
 Fleshy fruits and tubers require high K requirement
 By increasing the K supply to plant roots it is relatively easy to
increase the K concentration of various organs